docs: def _to_unit_base(self, base_unit, values, unit, from_unit):
          """Return values in a given unit given the input from_unit."""
          self._is_numeric(values)
          namespace = {'self': self, 'values': values}
          if not from_unit == base_unit:
              self.is_unit_acceptable(from_unit, True)
              statement = '[self._{}_to_{}(val) for val in values]'.format(
                  self._clean(from_unit), self._clean(base_unit))
              values = eval(statement, namespace)
              namespace['values'] = values
          if not unit == base_unit:
              self.is_unit_acceptable(unit, True)
              statement = '[self._{}_to_{}(val) for val in values]'.format(
                  self._clean(base_unit), self._clean(unit))
              values = eval(statement, namespace)
          return values